Marking instruments in the form of crayons have been used by young and old for decades. Historically, crayons have been manufactured by mixing together a binder, typically, a molten wax, and a suitable pigment. The molten mixture would be extruded into a desired shape, such as a cylinder, and subsequently cooled to a solid. The resulting crayon, when rubbed on a surface, such as paper, would leave a mark, i.e., a residue of pigmented wax, on the surface.
Over the years, the crayon has undergone a number of changes to improve its appearance, mechanical and marking properties, and toxicity. One of these changes, which affects the appearance of the crayon and the mark that it leaves on a given surface, is color. A wide variety of vivid and attractive colors has been enabled over the years through the development of new pigments. The increase in the number of colors and hues available in the form of a crayon has fueled the demand for further improvements in crayon properties, generally.
One aspect of crayon technology that has undergone significant change over the years is the composition of the binder component. The natural waxes, which were historically used as binders, have been improved through blending and the inclusion of additives. In addition, synthetic materials have been developed to provide, among other advantages, a more uniform distribution of pigment throughout the crayon, which translates into a more uniform distribution of pigment throughout the crayon mark and the ability to effect a mark on a wider range of surfaces.
Another aspect of crayon technology that has undergone significant change over the years is that of "special effects." For example, one special effect that has been attained is phosphorescence. Phosphorescence has been achieved through the introduction of phosphors, substances that emit light when excited by radiation, into the marking composition. Another special effect that has been attained is fluorescence. Fluorescence is attained by the introduction of fluorescers, substances that emit electromagnetic radiation, usually as visible light, resulting from and occurring only during the absorption of radiation from some other source. Other special effects include the introduction of glitter.
Thermochromic dyes, i.e., dyes whose color is sensitive to temperature, and pH- and bleach-sensitive dyes, i.e., dyes whose color is sensitive to pH or bleach, respectively, have been employed in other types of marking compositions to achieve the special effect of color change. For example, U.S. Pat. No. 5,232,494 discloses an aqueous coloring composition system for use in markers, wherein one composition contains a dye whose coloring ability is destroyed in the presence of a bleach, which is contained in a second composition for application on top of a mark generated with the first composition. Such a system which employs an aqueous composition is not, however, suitable for inclusion in a crayon. U.S. Pat. No. 3,957,495 discloses a solid writing material containing a colorless, electron donative, chromogenic compound, which develops color upon contact with a writing surface previously coated with an electron accepting substance. Accordingly, this system requires a specially coated writing surface, such as paper or polyvinyl chloride film, in order to achieve a colored mark on the writing surface with the solid writing material.
Special effects aside, the formulation of any marking composition intended for use in the form of a crayon should be such that it produces a crayon with good appearance, mechanical and marking properties, and relatively low toxicity. More particularly, a crayon should advantageously possess sufficient mechanical strength so that it can successfully withstand rubbing on a surface without undue crumbling or breaking. Moreover, the crayon, when rubbed on a surface, should advantageously provide a relatively uniform laydown, i.e., a relatively smooth and uniform layer of the crayon composition on the surface--without undue flaking. Further, the crayon should provide a mark that is substantially clean, and uniform, in coloration. In addition, the crayon should not be unduly hygroscopic in nature, i.e., it should not absorb water to the extent that it acquires a wet feel and loses mechanical strength.
Obtaining an overall satisfactory marking composition with respect to all of these properties, however, is not an easy task. Rather, new crayon formulations, particularly those into which have been introduced special effects, have been found to be fraught with problems, mainly due to the undesirable interactions between components never before combined together in a crayon composition.
It is, therefore, an object of the present invention to provide a marking composition system, which is suitable for use in the form of crayons and pencils and which provides a special effect.
Another object of the present invention is to provide a special effect marking composition system capable of generating a high quality mark on a variety of surfaces.
Yet another object of the present invention is to provide a special effect marking composition system with good mechanical strength.
Still another object of the present invention is to provide a special effect marking composition system with good appearance.
A further object of the present invention is to provide a special effect marking composition system with relatively low hygroscopicity.
An even further object of the present invention is to provide a special effect marking composition system with relatively low toxicity.
These and other objects and advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.